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Mr. Lee Sampson <br /> April 23, 2021 <br /> Page 8 <br /> Design Mining Height, ft <br /> Depth of Cover, ft 3 3.5 4 I 4.5 5 1 5.5 1 6 6.5 7 7.5 8 8.5 9 <br /> 110 49 53 581 621 661 70 73 77 81 84 87 91 94 <br /> 130 55 59 641 681 731 77 81 85 89 93 97 101 104 <br /> 150 62 66 701 741 791 84 89 93 98 102 106 110 114 <br /> 170 68 73 781 821 861 91 96 101 106 110 115 120 124 <br /> 190 741 801 85 90 95 99 1041 108 1131 119 124 129 134 <br /> 210 80 86 92 98 1031 108 113 118 122 127 132 137 143 <br /> 230 86 93 99 106 112 117 123 128 133 138 143 148 152 <br /> 250 91 99 106 113 120 126 132 138 144 149 155 160 165 <br /> 270 97 105 113 121 128 135 142 148 154 161 166 172 178 <br /> 290 103 112 120 128 136 144 151 158 165 172 178 185 191 <br /> 310 108 118 127 136 144 152 160 168 175 183 190 197 204 <br /> 330 113 124 134 143 152 161 170 178 186 194 202 209 217 <br /> 350 1191 1301 140 1501 160 170 179 1881 196 205 213 221 229 <br /> Coal strength, psi 495 Mining width, ft 11.50 No. web pillars 19 <br /> Pillar widths in italics have width-to-height ratios of 0.8 <br /> 240 20 <br /> 228 19 <br /> 216 18 Mining <br /> Height, <br /> 204 17 ft <br /> 192 16 t 3 <br /> 180 15 w 3.5 <br /> 168 148 No 4 <br /> Q 156 134 �4.5 <br /> 5 <br /> CL 144 12a <br /> 5.5 <br /> 132 11�: 6 <br /> 120 CY 105 6.5 <br /> a <br /> 108 + ' 9 �a 7 <br /> 96 + 8 -7.5 <br /> 84 7 8 <br /> 8.5 <br /> 72 ++ 6 <br /> 9 <br /> 60 5 <br /> 48 4 <br /> 110 130 150 170 190 210 230 250 270 290 310 330 350 <br /> DEPTH OF COVER,ft <br /> Figure 3a. Web Pillar Design Chart—Collom B2/B3 Seam <br /> Agapito Associates, Inc. <br />